In the preceeding years of this project we have developed a unique instrument to noninvasively assess the concentration and morphology of transfusion platelets in a rapid clinically acceptable procedure. The basis of this measurement is low-angle multiple scattering of light and the changes in this signal associated with orientation of the subset of the platelet population that are discoid. The instrument, as developed, is automated under microprocessor control and calculates the clinically important values of concentration and percentage that are discoid of the platelets in transfusion bag within a 3-minute period. These highly accurate measurements are being used in a variety of research studies of the effects of various storage conditions (e.g., temperature transients, bag wall material, addition of pharmacological agents) on the condition of stored platelet concentrates. The instrument was originally designed to play a significant role in improving the quality of platelet transfusions, by routine and accurate noninvasive assessment of platelet transfusions, by routine and accurate noninvasive assessment of platelet quality (as represented by the degree or normal platelet morphology). To this purpose ongoing studies at the Univ. of Va. Medical School Blood Bank are directed at its clinical utility and determining the degree of correlation of the noninvasive measurement with clinical efficacy of the platelet transfusion.